Isoindigo-based conjugated polymers, PII2T-C6 and PII2T-C8, with carbosilane side chains have been designed and synthesized for stretchable electronic applications. The carbosilane side chains offerred a simple synthetic pathway to evaluate long and branched side chains in high yields and were prepared with a six or eight linear spacer plus two hexyl or octyl chains after branching. The studied polymers showed a high charge carrier mobility of 8.06 cm2 V–1 s–1 with an on/off current ratio of 106 as probed using a top-contact transistor device with organized solid state molecular packing structures, as investigated through grazing-incidance X-ray diffreaction (GIXD) and atomic force microscopy (AFM) technique systematically. The studied polymers, more attractive, exhibited superior thin film ductility with a low tensile modulus in a range of 0.27–0.43 GPa owing to the branched carbosilane side chain, and their mobility was remained higher than 1 cm2 V–1 s–1 even under a 60% strain along parallel or perpendicular direction to the tensile strain. Such polymer films, in addition, can be simultaneously operated over 400 stretching/releasing cycles and maintained stable electrical properties, suggesting the newly designed materials possessed great potential for next-generation skin-inspired wearable electronic application with high charge carrier mobility, low tensile modulus, and stable device characteristics during stretching.

Carbosilane side chain-equipped isoindigo−bithiophene semiconducting polymers (PII2T) have been designed and synthesized for stretchable electronics applications. Systematically tailoring the length and branch position of carbosilane side chains (C6 to C10) offers an effective route to optimize charge-transport behavior and improve the mechanical properties of semiconducting polymer thin films. The basic polymer properties, surface morphology, electrical characteristics, and strain-dependent performance of polymers with various lengths of carbosilane side chains were explored. The series of polymers exhibited a field-effect mobility over 2 cm 2 V −1 s −1 , and an odd−even effect was observed relating to the length of side chains. On the other hand, when the longer side chain was incorporated, a lower thin-film modulus was reached because the extended side chain can dilute the volume of the rigid polymer backbone and open up the space between polymer chains (i.e., larger lamellar spacing). Surprisingly, PII2T-C10 thin films possess desirable electrical and mechanical properties, achieving a mobility of 1 cm 2 V −1 s −1 even when stretched under 100% strain, which is the best electrical performance among intrinsically stretchable conjugated polymers in the research community.

Biaxially-extended thiophene–isoindigo donor–acceptor conjugated polymers were explored for high-performance flexible field-effect transistors. A charge carrier mobility of 1.0 cm2 V−1 s−1 was achieved under ambient atmosphere with stable electrical properties.

Biaxially thiophene side chain extended thieno [3,2b]thiophene (TT2T)-based polymers, PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T, were synthesized by Stille coupling polymerization with different conjugated moieties of thiophene (T), bithiophene (2T), thieno[3,2-b]thiophene (TT), and thiophene− vinylene−thiophene (TVT), respectively. The electronic properties of the prepared polymers could be effectively tuned because the variant πconjugated building block affected the backbone conformation and the resulted morphology. The morphology of the thin films characterized by atomic force microscopy and grazing incidence X-ray diffraction showed that P2TTT2T and PTVTTT2T thin films possessed a better molecular packing with a nanofiber structure owing to their coplanar backbone. The average field-effect mobilities of PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T were 6.7 × 10 −6 , 0.36, 2.2 × 10 −3 , and 0.64 cm 2 V −1 s −1 (maximum 0.71), respectively, attributed to the coplanarity of polymer skeleton. In addition, the fabricated FET devices showed a high on/off ratio over 10 7 under ambient for over 3 months, suggesting the excellent environmental stability. The above results demonstrated that the biaxially extended fused thiophene based conjugated polymers could serve as a potential candidate for organic electronic device applications.